Nerve Regeneration after Refractive Surgery
Helsinki University Eye Hospital
Purpose: To describe the morphology of neural damage induced by LASIK and PRK and both morphological and functional recovery of nerves, and to discuss the significance of these phenomena in corneal refractive surgery.
Method: A review based on primary observations based on histological or in vivo confocal microscopical studies and two recent reviews (EER 2003;76:521-542; PRER 2003;22:339-358).
Results: Sensory, sympathetic and parasympathetic nerves have been found in animal cornea, the first two types of nerve fibres in human cornea. These contain a variety of nerve transmitters with potential of regulating wound healing and or inflammation/tissue responses. PRK, LASIK and PRK severe corneal nerves leading to loss of sensitivity, impaired lacrimation and neurotropic epithelial changes. Following PRK signs of neural regeneration appear during the first postoperative days. Functional regeneration takes several months but may reveal subnormal. Nerve anatomy often reveal abnormalities even years after PRK. Corneas examined 5 years after PRK may reveal abnormalities probably due to absence of the Bowman´s layer. Changes in keratocyte phenotype are common and variable. LASIK is followed by functional impairment comparable to PRK but more normal subepithelial plexus. However, stromal nerves penetrate the wound margins poorly after both LASDIK and PKP. Epikeratophakia induces remarkable neural pathology. Relatively normal innervation has described after introduction of INTACTS.
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